In mathematics, a closed form expression or formula is one that is formed with constants, variables, and a set of functions considered as basic and connected by arithmetic operations and function composition. Commonly, the basic functions that are allowed in closed forms are nth root, exponential function, logarithm, and trigonometric functions. However, the set of basic functions depends on the context. For example, if one adds polynomial roots to the basic functions, the functions that have a closed form are called elementary functions.